Flash isn't doomed quite yet. Flash supplanted java as the primary form of interactivity on the web in the early years, and javascript + html has been making inroads but flash still has a significant advantage. Pure HTML/CSS/JS/Canvas/SVG designs are nearly as capable as flash, but there are still serious design defects in the system, major problems with client support and standardization, and a distinct lack of tooling.

Today it takes a not insignificant amount of effort just to make a simple text box with a border having 4 rounded corners that displays correctly for >90% of a site's visitors using pure html/css techniques. Even if every internet user upgraded to a modern, standards compliant, CSS3 supporting browser tomorrow, there would still be a substantial hill to climb for designing good looking pure html/css sites, it would just be a slightly smaller hill.

Almost certainly this will change, standards will get better, browser marketshare will continue to skew toward newer browsers, tooling will improve, but all of these things will take time.

This is not a defense of flash, I don't think flash is good for the web even today, but until the very real problems of pure html/css design are put to rest (CSS4?) flash will still be seen as a go-to technology for a lot of things people want to do with the web.